MFC r191164

MFC r191164

Prevent atkbd(4) interrupt handler from calling keyboard callback function
when polled mode is enabled. This should help with duplicated/missing
characters problem at mountroot, geli, etc. prompts on multi CPU systems
while kbdmux(4) is enabled.

Tested by:	Tobias Grosser <grosser -at- fim -dot- uni-passau -dot- de>
Tested by:	Fabian Keil <freebsd-listen -at- fabiankeil -dot- de>
Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/releng/7.2@191327 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f